The present invention relates to an improved height adjusting mechanism for use on a swivel chair which is provided with a screw shaft having an axial close-ended restraint groove, and a separable positioning ring block assembly including a ring block piece and an arc limiting piece that are easily matched into a ring form and received in a cavity at the top end of a shaft tube, and a cylindrical adjusting mount having a room at the bottom end thereof with a peripheral flange defined on the inner wall of the room, the flange is engaged with an extended connecting journal at the top of the shaft tube, making the assembly thereof easy and speedy. Such a close-ended groove can prevent disengagement of a ring block assembly from a screw shaft of a swivel chair due to excessive adjustment.
Swivel chairs have been popularly used in offices and places of the like because they provide comfort and facility in use. To make a swivel chair easily adjusted for people having different physical sizes to use, a prior art swivel chair, as shown in FIG. 1, is generally equipped with a height adjusting mechanism, as shown in FIG. 2.
Referring to FIG. 1, a conventional height adjusting mechanism of a swivel chair has a shaft tube 1, a shaft 2, a restraint ring member 3 and an adjusting mount 4. The shaft tube 1 has a tubular interior 11 in which the shaft 2 is housed. At the top end of the shaft tube 1 is disposed a journalled extension 12.
The shaft 2 with one end fixed to the center of the underside of a seat has an elongated groove 21 having either the upper end or lower end opened for easy fitting of the restraint ring member 3 slidably mounted onto the shaft with a protruded restraint piece 32 engaged with the elongated groove 21. The ring member 3 has a plurality of projection spots 31 on the top surface thereof.
The adjusting mount 4 having a through hole 41 for the passage of the screw shaft 2 is screwed onto the screw shaft. It has a room at the bottom end thereof for movable accommodation of the ring member 3. The ceiling of the room is provided with a downwardly extended projection 42, and a through hole 43 is disposed on the wall of the adjusting mount 4 so as to permit the mount 4 to be securedly engaged with the journalled extension 12 by way of a screw 44.
A conventional height adjusting mechanism is assembled in a way as described above. When a person sits on such a chair and swivels, the weight thereof forces the projection 42 of the adjusting mount 4 in limiting engagement with the protruded restraint pieces 31 and the restraint ring member 3 with the restraint piece 32 in engagement with the groove 21 is stopped from rotation, the screw shaft 2 rotates inside the shaft tube 1 without lifting or lowering with respect the adjusting mount 4. As the seat of a swivel chair is free, the adjusting mount 4 is not engaged With the restraint ring member 3 so that the ring member 3 along with the screw shaft 2 can be spinned together as the seat is rotated for adjustment of the height thereof.
The prior art height adjusting mechanism has the following disadvantages in operation, they are given as below:
1. The restraint ring member 3 having a projected restraint piece 32 is integrally made and can not be engaged with the elogaged groove 21 of the screw shaft 2 if the groove is not provided with an open end. However, the open ended groove 21 will cause the ring member 3 to easily separate from the screw shaft 2 accidently due to excessive adjustment, resulting in a separation of a seat from the screw shaft 2. PA1 2. The adjusting mount 4 is secured to the shaft tube 1 by a screw. Most adjusting mount is made of plastics, so after a period of time, the adjusting mount is easily damaged or worn out.